Late aneurysms are common after repair of coarctation of the aorta by prosthetic patch aortoplasty but are rare after subclavian flap aortoplasty. We present the case of a 14-year-old boy who underwent a grafting procedure for a descending thoracic aortic aneurysm after subclavian flap aortoplasty for coarctation of the aorta when he was 2 years old. This is the fifth report of late aneurysm formation after subclavian flap aortoplasty.